Binders or binder systems for foundry cores and molds are well-known. In the foundry art, cores or molds for making metal castings are normally prepared from a mixture of an aggregate material, such as sand, and a binding amount of a binder or binder system. Typically, after the aggregate material and binder have been mixed, the resulting mixture is rammed, blown or otherwise formed to the desired shape or pattern, and then cured with the use of catalysts and/or heat to a solid, cured state.
A variety of different processes for forming molds and cores have been developed in the foundry industry One type of process known as the "hot-box" process requires that the mixture of aggregate material and binder be cured and hardened in a holding pattern or core box while subjected to heat. Another type of binder system which does not require heating in order to bring about curing or hardening is known as a "no-bake" process. A third type of process used for forming molds or cores is known as the "cold-box" process. "Cold-box" processes are generally carried out by passing gaseous catalysts or hardeners through molded resin-coated sand at ambient temperatures in order to achieve curing.
Resins cured with acids or acid salts have been used in both the hot box and no bake processes. Such acid cured resins include both phenolic and furan resins as well as mixtures of these with other resins. Akaline solutions of phenolic resole resins have been used as binders in both no bake and cold box processes. When such alkaline phenolic resole resins are used in the no bake process, they are cured by the addition of a liquid ester hardener. When the alkaline phenolic resole resin binders are used in the cold box process, they are cured by means of a gaseous or vaporized ester hardener.
Sands coated with alkaline phenolic resole and acid-curable resins tend to have less flowability than sands coated with certain other binder systems This can adversely affect quality of the foundry cores and molds. In the case of the cold box process, higher blow pressures are needed to blow the coated sand into the core boxes and it is more difficult to blow uniformly dense cores.
Now it has been found, in accordance with this invention, that the use of certain surfactants improves the flowability of sands coated with alkaline phenolic resole and acid-curable resin binders. These sands form cores and molds with smoother surfaces and sharper edges, as well as with more uniform density. Such cores and molds give castings of better quality. This improvement also makes possible the production of cores and molds with more delicate patterns. Furthermore, when the resin coated sands of this invention are blown into core boxes, they can be blown at lower pressures resulting in less pattern wear and in less sand being blown out of the vents. In addition, the cores prepared from these sands are released more readily from the core boxes.